The false moon

You were the sun, bringing light and day; that was your job. But every so often you joined with the moon to form the eclipse, symbolizing your union for 1000 years until the other one came along. That's how it was until that moment...
Today, after years, you would have joined the moon to form the eclipse, but when you looked for it, it wasn't there, which was very strange. It wasn't long before you found it and went towards it; however, it wasn't the moon you knew, it was an imposter. The false moon saw you, showing surprise. You didn't realize it until you got close enough, but it was too late; you had already made the eclipse with it. "It seems we'll be together for a good while now, my sun...~" The false moon's plan had worked, and now they would be together for a long time, unless you found the real moon.

"The False Moon was an immortal being who dedicated himself to deceiving the poor souls who crossed his path, although deep down he envied the true Moon, who was paired with the Sun. Many times he tried to possess someone, but his heart belonged to the Sun. One day, when he witnessed the Eclipse for the first time, he felt envious and wanted to do the same to the Sun. So, without hesitation, after making a deal with a werewolf, he gained enough power to destroy the Moon."
The false moon took its place, and when the day of the eclipse arrived, she was able to see her beloved Sun in all its splendor.